The present invention generally relates to manufacturing optical fiber cables and, more particularly, to a torque capstan that improves the consistency of the reverse oscillating lay of the cables during the manufacturing process, thereby improving the quality of the manufactured cables.
It is known in the optical fiber cable manufacturing industry that reverse oscillating lay (ROL) inconsistency during the cable manufacturing process, particularly in regard to high-fiber-count (HFC) cables, results in non-uniform distribution of the mechanical load and stress on the cable throughout its entire length. This non-uniform distribution of mechanical load/stress on the cable during the manufacturing process often results in the cable exhibiting high optical loss during mechanical and environmental qualification tests, which is regarded as a failure in the cable.
FIG. 1 is a graphical representation illustrating the manner in which a HFC cable 1 twists during a typical HFC cable manufacturing process. A HFC cable 1 is a cable that comprises a plurality of subunits 2, typically three to twelve, each of which comprises a plurality of coated optical fibers (not shown). During the manufacturing process, a reverse oscillating lay (ROL) machine is used to create the proper amount of ROL in the HFC cable. A portion of an ROL machine used for this purpose is shown in FIG. 2. During the HFC cable manufacturing process, the subunits 2 of the HFC cable are pulled through holes 5 formed in a series of reverse oscillating plates 6 as adjacent reverse oscillating plates are rotated in the same direction, but at incrementally increasing angles of rotation. At a particular point during the rotations of any two adjacent plates 6, a predetermined amount of twist is added to the core of the HFC cable. At this point, the direction in which each of the plates is being rotated reverses, and the plates rotate oppositely until the same amount of twist has been added to the core of the HFC cable in the opposite direction. The twisting of the HFC cable in this manner as it is being pulled is intended to equalize the distribution of stress on the subunits over the length of the cable.
With reference again to FIG. 1, the lay length is a length of a complete 360xc2x0 turn of the cable core in either the clockwise 3 or counterclockwise 4 directions. Once the apex is reached in either direction, the adjacent plates 6 reverse their directions of rotation and a transition 5 occurs in the cable 1 when the twisting direction changes. The ROL value corresponds to the desired lay length that is typically programmed into a control system of the ROL machine. Ideally, the measured lay length at any point during the manufacturing process should be equal to the programmed ROL value.
In current HFC cable manufacturing processes, after the cable leaves the ROL machine, it is pulled through a powder machine (for certain cable types), a set of torsion rolls that helps to keep subunits 2 together, and an extruder (not shown), which extrudes a material over the sub-units to form the outer jacket of the cable. As the HFC cable leaves the extruder, it is pulled through, respectively, a water trough and a main capstan. The water trough cools and solidifies the extruded material to form the outer jacket of the HFC cable. The main capstan provides the pulling force and controls the speed at which the cable is pulled along the manufacturing line.
One of the problems associated with known HFC manufacturing techniques is that they often do not ensure that the ROL is consistently maintained (i.e., that the programmed ROL value=the measured lay length), which causes non-uniform stress distribution in the cable. This often results in the cable failing during testing or usage due to high optical loss.
Accordingly, a need exists for a way of ensuring that the ROL is consistently maintained during the manufacturing process, thereby decreasing or eliminating cable failures that often result from ROL inconsistency. The present invention provides a torque capstan for use in an optical fiber cable manufacturing process which enables reverse oscillating lay (ROL) length to be maintained. The torque capstan comprises a first portion having at least two pulleys rotationally mounted thereon, a second portion having at least two pulleys rotationally mounted thereon, and first and second drive belts mounted on the pulleys of the first and second capstan portions, respectively. Rotational motion is imparted to the first and/or second drive belts through a drive system that is coupled to a drive pulley of at least one of the first and second capstan portions. Rotation of the drive pulley(s) causes the respective drive belt to rotate in a direction parallel to, or substantially parallel to, a direction in which an optical fiber cable being manufactured in the optical fiber cable manufacturing process is being pulled. Contact between the drive belts causes the drive belts to rotate in the same direction. At least one of the first and second drive belts has a longitudinal groove formed therein that is parallel to, or substantially parallel to, the direction in which the optical fiber cable is being pulled. The belts grip the cable in such a way that the ROL length is maintained over a length of the optical fiber cable, thus improving the quality of the manufactured optical fiber cables.
In accordance with one embodiment, each of the upper and lower drive belts of the capstan have the grooves formed in them longitudinally with respect to the direction in which the cable is pulled during the cable manufacturing process. Each of the grooves has a cross-sectional shape designed such that, when vertical force is placed on each of the drive belts in opposite directions, the grooves of the drive belts are pushed towards each other and about the cable. The grooves together form an annulus opening that is adapted to grip the cable in such a way that the subunits are properly kept together and lay lengths in the cable, which are produced by the ROL machine, are maintained, or substantially maintained, before cable enters the extruder.
In accordance with one embodiment, the capstan is utilized in conjunction with a capstan feedback control system that controls the torque placed on the cable by the capstan in order to offset excessive back-tension produced by the ROL machine and by a subunits payoff machine. In accordance with the present invention, it has been determined through experimentation and analysis that the excessive back-tension placed on HFC cables during the manufacturing process, as well as significant periodical fluctuations of the tension force amplitude during the manufacturing process, result in ROL inconsistency and ineffectiveness in lay capturing. By offsetting the excessive back-tension produced by the ROL and payoff machines in accordance with feedback signals relating to the amount of tension being placed on the cable, excessive back-tension and significant periodical fluctuations of the tension force amplitude are reduced or eliminated, thus improving ROL consistency and lay capturing. These features of the present invention, alone and/or in combination, result in an overall improvement in the quality of the manufactured cables.
These and other features and advantages of the present invention will become apparent from the following description, drawings and claims.